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About RAID

Last updated 2014-01-04 - Send Feedback
Related: Storage, storage, RAID

RAID can be implemented in hardware or software.

Most computer users do not use RAID at all, using instead independent hard drive or SSD storage. That approach is least expensive and fine for most uses.

RAID is not for backup

The fault tolerant aspect of some types or RAID should not be confused with a proper backup strategy.

It’s not that RAID (e.g., a mirror) is a bad idea for backup, rather, it is generally a waste of money and a reduction in redundancy: it is always better to have multiple independent redundant backups than one RAID backup.

For example, two independent backup drives of 4TB each are better than one RAID-1 mirror single unit. In the dual case, failure of one unit leaves the other intact and they can be stored separately, further reducing risk; in the single-unit RAID-1 case, loss of the unit means all is lost (consider theft, fire, flood, etc).

Why use RAID?

For professionals, higher performance and/or fault tolerance might be helpful or even essential, and that is where RAID comes into the picture.

RAID compared using four 4TB drives
  RAID-5 RAID 1+0 RAID-0 stripe RAID-1 mirror RAID SPAN JBOD
# Drives 4 4 4 4 4, concatenated 4
independent
non-RAID
Capacity: 12TB 8TB 16TB 4TB 16TB 16TB
Fault tolerance: single failure OK single failure OK
from each mirror
single failure kill volume three failures OK single failure kills volume independent
Read Speed ~3X 2X 4X 1X 1X, variable 1X
Write Speed 2.2X - 3X 2X 4X 1X 1X, variable 1X

Relative performance of RAID- vs RAID-5

See RAID-5 vs RAID-0 performance.

ThunderTek/PX Q6G: RAID-0 striping vs RAID-5

 

 


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